Acne vulgaris is a skin condition that affects over 85% of all people. Acne is a term for a medical condition of plugged pores typically occurring on the face, neck, and upper torso. Following are four primary factors that are currently known to contribute to the formation of acne vulgaris; (1) increased sebum output resulting in oily, greasy skin; (2) increased bacterial activity, normally due to an overabundance of Propionibacterium acnes bacteria; (3) plugging (hypercornification) of the follicle or pilosebaceous duct; and (4) and inflammation. The plugged pores result in blackheads, whiteheads, pimples or deeper lumps such as cysts or nodules. Severe cases of acne can result in permanent scarring or disfiguring.
Though acne vulgaris is multifactorial, a commensal skin bacteria (P. acnes) plays a major role in the formation of acne lesion. It is an infection of pilosebacious glands, oil glands in the skin. In most cases sudden breakouts of acne can be correlated with sudden increased production of sebum in the affected individual. During adolescence androgen hormones play a crucial role. It leads to overproduction of sebum by the pilosebaceous gland. The situation gets further accentuated by irregular shedding of dead skin from lining of hair follicles. As the dead skin cells clump together in the oily environment, they can form plugs which block the pores of the hair follicles. A pore clogged by the shedding skin is referred to as a comedo.
This creates a very conducive anaerobic condition for P. acnes bacteria to grow. Hyperproliferation of P. acnes leads to destruction of follicular walls and it sends a danger signal to the host immune system. P. acnes may trigger an innate immune reaction both in very early (microcomedogenic) and in late (inflammatory) acne lesions via the activation of Toll like receptors 2 (TLR2) on inante immune cells. TLR activation ultimately triggers the expression various cytokines (like IL-6, IL-8, IL-12, IL-17 etc) and chemokines that stimulate recruitment of other host immune cells [Jeremy et al, 2003; Thibout et al, 2014]. Acne lesions range in severity from blackheads, whiteheads and pimples to more serious lesions such as deeper lumps, cysts and nodules.
Although various over-the-counter products are commercially available to counteract acne condition, such as anti-acne agents for topical use, including salicylic acid; sulfur; lactic acid; glycolic acid; pyruvic acid; urea; resorcinol; N-acetylcysteine; retinoic acid; isotretinoin; tretinoin; adapalene; tazoretene; antibacterials such as clindamycin, tetracyclines, and erythromycin; vitamins such as folic acid and nicotinamide; minerals such as zinc; benzoyl peroxide; octopirox; triclosan; azelaic acid; phenoxyethanol; phenoxypropanol; and flavinoids, these agents tend to lack in potential to mitigate the acne condition and may have negative side effects when devised in conventional topical formulations. A key challenge that has limited the use of topical formulations is the absence of formulations with the desired physicochemical properties and high drug loading, which maintains a concentration significantly higher than the MIC at the site of application by facilitating the right degree of penetration over time but with minimal systemic exposure. A formulation that addresses these unmet needs can be a significant advance in the treatment of acne.
Furthermore, as articulated in [Taglietti et al, 2008], when it comes to the delivery of a drug to a specific site, topical formulations that are efficacious are probably among the most challenging products to develop. Once the product is applied on the skin, a complex interaction occurs between the formulation, the active compounds, and the skin itself. The penetration of the active compound(s) into the skin follows Fick's first law of diffusion, which describes the transfer rate of solutes as a function of the concentration of the various ingredients, the size of the treatment surface area, and the permeability of the skin. However, the skin's permeability can be influenced by many factors, such as the drying, moisturizing, or occluding effects of the excipients in the formulation, which, in combination, can modulate the release of the product at the treatment site. In acne, the site of action is inside the pilosebaceous unit and, therefore, an efficacious anti-acne formulation should facilitate the penetration of the active compound(s) into this extremely lipophilic environment. An effective topical formulation therefore needs to provide a stable chemical environment in a suitable dispensing container in order to accommodate multiple compounds that may have different, if not incompatible, physicochemical characteristics [Tagleitti et al, 2008]. Once applied, a topical formulation must interact with the skin environment, which can influence the rate of the release of the compound(s) in order to achieve adequate skin absorption, and exert additional physical effects on the skin, such as drying, occluding, or moisturizing [Tagleitti et al, 2008]. For example, even if an active agent is very potent, and is effective via a systemic route, in the case of topical administration can behave completely differently, i.e. if the desired concentration is not reached in the pilosebaceous (or skin) unit, it will not serve as an effective anti-acne therapy. Similarly, a molecule or drug can behave entirely differently if formulated with different compositions, which we demonstrate later in an example. Similarly, two molecule or active agents may behave entirely differently in the same formulation or composition. Therefore, every new molecule that needs to be formulated for topical skin application poses a novel and independent challenge as it is impossible to predict which composition and ratio of active and excipients will provide the desired efficacy benefit.
Furthermore, an emerging condition is the evolution of strains of P. acnes, which do not respond to the antibiotic agents such as clindamycin, tetracyclines and erythromycin currently approved for the treatment of acne. While the earlier dogmawas that antibiotics failure arises due to selection of ‘resistant’ strains, i.e. a mutation resulting in alteration of the target of the antibiotic rendering it ineffective, emerging evidence suggests that antibiotic failure is more complex than this simple understanding. The assumption was that if resistance develops, i.e. the target of an antibiotic is altered, it is possible to treat the condition by changing to an alternative antibiotic, the target of which is still intact in the bacteria. However, recent knowledge has rendered this assumption as false. For example, Regoes et al, 2004 demonstrates that even in the absence of any resistance, a subset of bacteria can just exhibit tolerance to an antibiotic, i.e. not undergo lysis. This could arise due to physiological (metabolic) and morphological changes observed in bacteria exposed to antibiotics. For example, in a study published in Science, [Miller et al, 2004] showed that a transient induction of SOS response by ampicillin can protect E. coli against the bactericidal effects of ampicillin. Regoes et al, 2004 suggested that tolerance mechanisms could cross over between some antibiotics, i.e. Antibiotic A might be rendered ineffective due to development of resistance, but it is possible that Antibiotic B, which has an entirely different target/mechanism of action, and is shown to be active in a different or sensitive bacterial strain, may also be rendered ineffective in the resistant strain due to shared tolerance mechanisms. Indeed, massive changes in gene expression leading to alteration in the syntheses of proteins of metabolic and stress response pathways and cell division during exposure of E. coli to ampicillin and ofloxacin have been observed, and a number of these alterations in the gene expression levels were shared between bacteria exposed to ampicillin and ofloxacin, suggesting a bacteria not responding to ampicillin may not respond to ofloxacin although both agents have different targets. We saw a similar observation in screening a library of antibiotics against different strains of P. acnes that are sensitive or non-responsive to clindamycin (a lincosamide). As shown in FIG. 1A, the strain of P. acnes non-responsive to clindamycin also showed increased survival capability in the presence of roxithromycin (a macrolide), which targets a different site from clindamycin. [Keren et al, 2004]. Specialized persister cells and the mechanism of multidrug tolerance in Escherichia coli. J. Bacteriol. 186:8172-8180) suggested that random fluctuations in gene expression are responsible for the formation of specialized persister cells. As argued by Regoes et al, 2004, phenotypic tolerance to antibiotic could actually prevent clearance. As a result, while there remains a need in the art for compositions, formulations and methods for treating acne that is not responding to the currently used agents, especially clindamycin-, minocydine-, erythromycin-, and/or doxycycline, the probability of tolerance makes itimprobable to predict a drug that may work against P. acnes. 
Furthermore, it is increasingly becoming evident that subtle changes in chemical structure of a molecule can dramatically change activity of the molecules against target protein. For example erythromycin (a macrolide) and clindamycin bind to similar 50S ribosomal unit but crystal structure [Schulzen et al, 2001] showed different mode of binding between the agents and amino acid residues present in 50S ribosomal sub-unit. There are known bacterial strains of P. acnes that are resistant to clindamycin but can be either non-responsive or susceptible to erythromycin and vice versa. Interestingly, telithromycin, which is a semisynthetic derivative of erythromycin works well in a bacterial strain that is resistant to both erythromycin and clindamycin [Beitru et al, 2003]. Similarly, in another example, the introduction of 8-chloro group dramatically enhanced the potency of moxifloxacin but a similar change in gatifloxacin had no effect against S. aureus, S. pneumonia, and E. coli. Additionally, molecules of the same class can have different affinity for the same protein target but in different bacteria. For example it has been found that both besifloxacin and moxifloxacin effectively bind to DNA gyrase than ciprofloxacin in S. aureus. In contrary ciprofloxacin binding towards DNA gyrase is more effective in E. coli than moxifloxacin or besifloxacin. Similarly, besifloxacin is found to be best effective molecule against S. pneumonia followed by moxifloxacin and ciprofloxacin. [Cambau et al, 2009]. It is therefore not possible to predict the activity of a molecule against a bacteria or microbe based on its similarity in structure another drug that shows activity against the same microbe or a different microbe, even though they might have similar mechanisms of action. Indeed, as shown in FIG. 1, we observed that molecules that were verisimilar in structure had completely distinct activity against P. acnes, i.e. where one was inactive the other was very potent against both clindamycin-susceptible and -non-resistant P. acnes (FIGS. 1 A and 1B). In another example, which we discuss later, we observed a non-lincosamide molecule that was very effective in a P. acnes strain resistant to clindamycin but not active in a clindamycin-sensitive P. acnes (FIGS. 1A and 1B). The identification of an effective drug that works against both sensitive as well as clindamycin-, minocycline-, erythromycin-, or doxycycline-nonresponder P. acnes therefore emerges through serendipity during systematic screening in P. acnes. 
Furthermore, while an emerging problem is the development of resistant strains of microbes that are not responding to antimicrobial compounds and compositions well known in the art, there remains a need in the art for a more effective antibiotic that not only works against resistant microbes but also reduces the risk of development of resistance by the microbes to this new antibiotic. Thus molecules that are efficacious antibiotics and also ‘prevent’ or reduce the development of resistance can be a major advancement in the treatment of microbial diseases.
The inflammatory character of acne has been correlated with the host immune response targeting Propionibacterium acnes, In vitro studies demonstrate that P. acnes whole cells or cell fractions stimulate cytokine and matrix metalloproteinase release from immune cells, keratinocytes, and sebocytes [Kim et al., 2002; Liu et al., 2005; Nagy et al., 2006; Lee et al., 2010] Though P. acnes are long been present in the follicular area, they come in direct contact with immune cells in dermis only after follicular rupture, The innate immune system recognizes P. acnes via TLR2 [Kim et al., 2002], leading to the secretion of inflammatory cytokines, including IL-6, IL-8, IL-12 etc. Follicular rupture happens very late in the disease process. But there are multiple evidences which suggest that the adaptive immune response also has a significant role in the inflammation observed even in early stages of acne, resulting from the recruitment of activated T helper 1 (Th1) lymphocytes to early acne lesions [Mouser et al., 2003]1. A potential treatment of acne therefore needs to resolve inflammation, and should be able to target these inflammatory pathways.
An ideal treatment for acne therefore need molecules that can work at two or more targets. Molecules that work against both antibiotic-sensitive as well as clindamycin-, minocycline-, erythromycin- and doxycycline-tolerant or non-responsive strains of P. acnes and can additionally inhibit the P. acnes-activated inflammatory mediator/s, or molecules that target two or more cellular targets in these microbes while additionally exerting an inhibitory effect on the P. acnes-activated inflammatory mediator/s, and is formulated in an optimal formulation that enables the desired concentration of the active agent on the skin or pilosebaceous region following topical application can emerge as a powerful strategy for the treatment of acne.